The present invention relates generally to a plate heat exchanger for a multiple circuit refrigeration system.
Heat exchangers, such as condensers and evaporators, are utilized in refrigeration cycles to exchange heat between a heat transfer fluid (e.g. water, brine or air) and a refrigerant. A single refrigerant circuit can be utilized in the refrigerant cycle. However, if the compressor needs service and is shut down, the refrigerant circuit cannot operate. Therefore, it is beneficial for two or more refrigerant circuits to be utilized. One refrigerant circuit may be switched off, allowing the other(s) to operate at full capacity or if service is required.
In a prior plate two pass heat exchanger, heat transfer fluid flows through alternate channels of the heat exchanger. In a heat exchanger having two refrigerant circuits, the refrigerant circuits are arranged so that all heat transfer channels exchange heat with both refrigerant circuits. At full load, both refrigerant circuits concurrently exchange heat with the entire heat transfer fluid flow. A drawback of the prior art is that heat exchanger is limited to a maximum of only two separate refrigerant circuits.
There are several drawbacks to the prior art plate heat exchangers for a multiple circuit refrigerant system. For one, when all of the refrigerant circuits are operating at a full load condition, the entropy generation (the destruction of availability) is high due to a relatively larger temperature differential between the heat transfer fluid and the refrigerant. Secondly, the difference between the saturated discharge temperature and the saturated suction temperature (temperature lift) is also high. The temperature lift is representative of the compression ratio and hence the compression power requirement.
Additionally, at part load condition, when one circuit is inactive, a significant portion of the liquid flow is not cooled in the inactive circuit. To meet the desired chilled liquid set point, the leaving liquid temperature from the active circuit needs to be significantly below the set point, placing an undue burden on the compressor and resulting in the loss of the coefficient of performance. When water is used as the heat transfer fluid, the leaving water temperature can approach the freezing temperature depending on the set point. The saturation temperature of the refrigerant may fall significantly below the freezing point temperature of the water, posing a threat of ice build up and failure of the heat exchanger.
Hence, there is a need in the art for an improved plate heat exchanger for a multiple circuit refrigeration system.
The present invention relates to a plate heat exchanger for a multiple circuit refrigeration system.
The plate heat exchanger of the present invention is formed from a plurality of alternating right plates and left plates adhered together by a method such as brazing, welding or gasket joints. The plates create a plurality of alternating heat transfer fluid flow channels and refrigerant flow channels. The heat transfer fluid flow channels pass through the entire length of the plate heat exchanger. In the preferred embodiment, the refrigerant flow channels include one or more seals located to create one or more separate refrigerant circuits. The heat transfer surface area of the refrigerant circuits are approximately proportional to the capacity of the compressor(s) connected to the circuits. For example, in a dual refrigerant circuit system, refrigerant from a first refrigerant circuit flows through the first portion of the refrigerant flow channels, and refrigerant from a second refrigerant circuit flows through the second portion of the refrigerant flow channels.
By employing a single heat transfer fluid circuit as described above, the average temperature difference between heat exchanging fluids can be reduced, reducing entropy generation and making the system more thermodynamically efficient. For the same amount of heat transfer area, the compressor power can be reduced significantly.
Accordingly, the present invention provides a plate heat exchanger for a multiple circuit refrigeration system.
These and other features of the present invention will be best understood from the following specification and drawings.